Generally, digital multimedia broadcasting (DMB) is a more enhanced digital broadcasting technique than a digital broadcasting technique for an audio only service, and DMB refers to a communication service for providing an audio service and a video service to a plurality of channels.
DMB provides high quality sound and pictures (similar or equal to CD or DVD quality) through a personal digital assistant (PDA) or a vehicle terminal that may be used while in motion. The DMB service is classified into a system A, a system Dh, and a system E.
System A is based on an orthogonal frequency division multiplexing (OFDM) applied to an SDMB and an European TDMB, and the system Dh uses a method for receiving a satellite DMB based on a terrestrial DMB. Also, the system E uses a code division multiplexing (CDM) method and is applied to a satellite DMB.
FIG. 1 is a block diagram showing a satellite DMB receiving apparatus based on a system E in accordance with the related art. As shown, the related art satellite DMB receiving apparatus comprises tuners 111 and 112, a CDM demodulator 120, a broadcasting information channel decoding unit 130, a broadcasting data channel decoding unit 140, a pilot channel decoding unit 150, a demultiplexer 160, and a decoder 170.
The tuners 111 and 112 demodulate a satellite DMB signal into a base band signal, and provides the base band signal to the CDM demodulator 120 for demodulation thereby extracting broadcasting information such as program specification information (PSI) and service information (SI). The CDM demodulator 120 provides the extracted broadcasting information to the broadcasting information channel decoding unit 130 for decoding using two Walsh codes1. The broadcasting information channel decoding unit 130 provides broadcasting data information such as video and audio data to the broadcasting data channel decoding unit 140. Also, the CDM demodulator 120 extracts control information of a receiver by using one Walsh code and provides the control information to a pilot channel decoding unit 150. 1 Walsh code is one of 64 chip patterns, which are 64 chips long, used to differentiate CDMA channels.
Each decoder 130, 140, and 150 uses Welch codes to decode the signal received from the CDM demodulator and then provides the resultant information to the demultiplexer 160.
The demultiplexer 160 demultiplexes information provided by each decoder 130, 140, and 150 and provides the output to the decoder 170, and the decoder 170 provides an images to a channel selected by a user.
As shown in FIG. 1, the broadcasting data channel decoding unit 140 of the related art satellite DMB receiving apparatus comprises a bit de-interleaver 141, a viterbi decoder 142, a byte de-interleaver 143, and a Reed-Solomon2 decoder 144. Each component comprises a pair for decoding two Walsh codes. 2 Reed-Solomon error correction is a coding scheme that works first by constructing a polynomial from the data symbol to be transmitted, and then by sending an over-sampled plot of the polynomial instead of the original symbol itself
The broadcasting data channel decoding unit 140 comprises a bit de-interleaver 141 for de-interleaving broadcasting data of a broadcast channel into a bit unit, a viterbi decoder 142 for decoding the deinterleaved broadcasting data of a broadcast channel coded into a convolution channel, a byte de-interleaver 143 for de-interleaving the decoded data into a byte unit, and a Reed-Solomon decoder 144 for decoding a byte outputted from the byte de-interleaver 143.
The broadcasting data decoded by the decoders 141 to 144 is demultiplexed by the demultiplexer 160 and provided to the decoder 170. The decoder 170 decodes the demultiplexed signal, thereby providing a video broadcasting signal for viewing.
However, the related satellite DMB receiving apparatus has the following problem. When the user switches to another broadcast channel while watching a first video broadcast channel, the CDM demodulator 120 performs a CDM demodulation for the Walsh code corresponding the new broadcast channel and decodes the demodulated broadcasting signal. The bit de-interleaving takes approximately 264 msec˜6.514 sec per bit to perform for a total bit-de-interleaving time of approximately 3.257 sec.
Accordingly, when changing from one broadcast channel of the satellite DMB receiving apparatus to another, the user experiences a delay of approximately 5˜8 seconds thereby causing difficulty in watching a video broadcast on the desired channel.